Gas springs of this kind are for example known from U.S. Pat. No. 3,656,593 and quite a number of subsequent publications of numerous variants. Because of their advantageous properties in particular as longitudinally adjustable lifting devices in chair columns and the like these gas springs have been extremely successful in practice. A small annular space is formed between the inner tube and the outer tube and serves as a relief space. The inner tube and the outer tube consist of steel, i.e. in particular of seamless drawn tubes, the internal wall of the inner tube still requiring a special surface treatment to achieve an impeccable sliding surface for the piston and for the seal located in the latter.
A longitudinally adjustable gas spring is known from DE No. 31 02 276 A1 having an outer tube and an inner hollow part located in the latter. A piston is slidably arranged in the hollow part and, sealed by a seal, bears against the internal wall of the hollow part; a piston rod is arranged on the piston and exits in a sealed manner at one end. A valve is provided at the other end. Two grooves are provided on the external wall of the hollow part, in which grooves tubes are arranged, which are introduced in a sealed manner into the valve and into the inner chamber of the hollow part adjacent to where the piston rod exits. This provides a construction wherein the gas spring substantially consists of one single body, namely the inner hollow part, with which the valve and the end on the side where the piston rod exits are integrally formed. In this case the outer tube only serves as means to provide a connection with the chair, table or the like to be supported. As compared with this the invention proceeds from that the whole gas spring is substantially defined, supported and axially held together by the outer tube -- as is usual with the longitudinally adjustable gas springs of the generic kind.